Two human infections with novel
influenza A viruses were detected in individuals from two states
(Indiana and Maine). Both patients were infected with swine-origin
influenza A (H3N2) viruses. One patient was hospitalized, but has now
been discharged and both continue to recover from their illnesses. Both
patients reported close contacts with pigs preceding their illness
onset.

The above comments are from the CDC’s
week 43 FluView which came out almost exactly one year after the
WHO pager alert on two trH3N2 cases in Illinois and
Pennsylvania. These two cases created considerable concern in
eastern Europe, which was answered by the CDC, who claimed no human to
human transmission, based in part on the sequence differences between
the two isolates, as well as the 6 weeks between disease onset
dates. More detail was provided in the first
“Have You Heard?” on trH3N2, which is used for background and
detail for the news media. These reports have specifics on
disease onset dates and some data on exposure.

The two current cases are significantly more alarming than the cases
described a year. The 2011 cases (A/Indiana/10/2011
and A/Maine/07/2011)
developed symptoms two days apart and two weeks after another case in
Maine, A/Maine/06/2011).
The sequences from the two Maine cases were virtually identical, and
the Indiana case had the same constellation of genes, some of which
were closely related to the two sequences from Maine, while others were
more closely related to the four July / August cases from Indiana (A/Indiana/08/2011
and Pennsylvania (A/Pennsylvania/09/2011,
A/Pennsylvania/10/2011,
A/Pennsylvania/11/2011).
However, all seven isolates had the same overall constellation of genes
which evolved
from the 2010 sequences and also acquired the M gene from
H1N1pdm09, and this constellation has never been reported in swine.

Although the CDC now cites no sustained human transmission, human to
human transmission has been acknowledged for the cluster in Minnesota,
as well as the first 2011 case (2M, A/Indiana/08/2011). However,
the absence of sustained transmission is based on negative data
generated by the same investigators and procedures that have failed to
identify a source for any of the 2011 cases. Thus, without
knowledge of how the confirmed cases were infected, there is no data on
other cases infected by the same source(s).

Moreover, there is little data supporting infection from a swine
“exposure”. The first case in Maine was from Cumberland County
and was said to have had swine exposure from attendance at an
agricultural fair in the week prior to symptoms on October 7.
This description matches the Cumberland County fair, which ended
October 1. However, the incubation period for influenza is short,
generally two days with a range of 1-4 days. Thus, the 6-7 day
gap between the swine exposure and onset of symptoms is outside of the
traditional incubation period.
This time gap is a greater issue for the Maine case described in the
week 43 FluView because the Maine CDC indicated the swine exposure for
the second case was also an agricultural fair, and media reports
indicated the Maine cases lived in the same area, suggesting the swine
exposure for the second case was also the Cumberland County fair, which
ended three weeks prior to symptoms. One of the cases
participated in a swine scramble (see video of the Oct 1
pig scramble).

Moreover, swine “exposures” for the earlier 2011 cases have no reports
of symptomatic swine. Media reports indicated the swine at the
Washington County fair were asymptomatic, and the early release MMWR
indicated the caretaker for the first case in 2011 was asymptomatic, as
were associated swine.

Thus, there are no reports of any of the seven 2011 cases being exposed
to symptomatic swine in the week prior to disease onset, and no swine
with a constellation of gene matching the seven cases have been
reported.